The Chicago Manual of Style, Strunk and White’s Elements of Style, most authorities on American English and Canadian English, and some authorities on British English (for example, Oxford University Press and Fowler’s Modern English Usage) recommend or require the use of the Oxford comma, also known as a serial comma.

Newspaper style guides (such as those published by The New York Times, The Los Angeles Times, the Associated Press, The Times newspaper in the United Kingdom, and the Canadian Press) recommend against it, possibly for economy of space.

IN GENERAL, OXFORD COMMAS ARE INTENDED TO RESOLVE AMBIGUITY:

The style that consistently uses the Oxford comma may be less likely to result in ambiguity. Consider the oft quoted, but (according to Snopes) mythological, book dedication:

To my parents, Ayn Rand and God.

There is ambiguity about the writer’s parentage, leading the reader to believe that the writer claims Ayn Rand and God are the parents. A comma before andremoves the ambiguity:

To my parents, Ayn Rand, and God.

But lists can also be written in other ways that eliminate the ambiguitywithout introducing the serial comma, such as using other punctuation, or none, to introduce or define them. For example, in the following manner:

To God, Ayn Rand and my parents.

I have used both styles in my writing, but am leaning more and more toward the Oxford comma.

Another wonderful example, reportedly collected by Nielsen Hayden, was found in a newspaper account of a documentary about country music legend, Merle Haggard:

Whoa! Who knew that Kris Kristofferson and Robert Duvall were Merle Haggard’s ex-wives? An Oxford comma would eliminate this hilarious inaccuracy:

Among those interviewed were his two ex-wives, Kris Kristofferson, and Robert Duvall.

I usually argue for consistent use of the serial comma because:

Use of the Oxford comma is consistent with conventional practice as suggested by the Chicago Manual of Style, which is my primary reference manual.

It matches the spoken cadence of sentences better, so reading passages aloud will flow more easily. This is something to consider if you intend to have your work turned into an audiobook.

Properly used, it resolves ambiguity.

Its use is consistent with other means of separating items in a list, for example, when consistently included before the last item even when and or or is present.

Its omission can suggest a stronger connection between the last two items in a series than actually exists. (My parents, Ayn Rand and God.)

Common arguments against use of the serial comma:

Improperly used, the comma may introduce ambiguity, and many authors are not clear on its proper use.

I agree that it can be redundant in a simple list because the words and & or can serve to mark the logical separation between the final two items, when the final two items are a compound single item. (My parents, Marge and Bob.)

When space is at a premium, the comma adds unnecessary bulk to the text—not usually an issue in a novel or short story. This is a journalistic issue common when writing for a newspaper.

It is fashionable for wouldbe writers to argue against using the Oxford comma, claiming it is unnecessary. However, I frequently see manuscripts where good authors fail to delineate a list in such a way that their intention is clear, by using and & or, thus resulting confusion, and a book that is less enjoyable than it should be.

The Oxford comma is the basis of many violent quarrels in writing groups–people tend to be rabidly for or against either side. There is common ground here, people so put away the torches!

Good writing incorporates proper use of both styles and, above all else, avoids ambiguity.